This invention relates to computer monitors and, more particularly, to a single horizontal scan range cathode ray tube (CRT) monitor for use with personal computers having differing output display signal formats.
There is little standardization among personal computer (PC) manufacturers for the resolution and frequency of the display signals generated by the display cards of the PCs. On the other hand, it is generally more expensive and complicated to make analog monitors which can adapt to a plurality of display signal frequencies. One such possible arrangement is shown in FIG. 1. In this arrangement a PC 10 includes a display card (not shown) having a digital to analog (D/A) converter 12 to output analog display signals, at a frequency and resolution set by the PC, to a CRT multiple scanning frequency monitor 14. The monitor 14 has to detect the frequency and adjust its scanning frequency to match that of the initial display signals. Such a monitor is complex and expensive to build.
Still another possible monitor display arrangement is illustrated in FIG. 2. Again the PC 10 includes a display card (not shown) having a digital to analog (D/A) converter 12 to output analog display signals, at a frequency and resolution set by the PC, to a single scan frequency liquid crystal display (LCD) monitor 16.
The LCD monitor 16 includes an A/D converter 18 that converts the received analog signals into digital signals. A scaling engine 20 within the LCD monitor 16 converts the digital display signals into a frequency and resolution that are compatible with the LCD monitor 16 and supplies them to a display circuit (not shown) within the LCD monitor 16. In this arrangement, the A/D converter and the LCD panel are expensive.
Yet another possible arrangement is illustrated in FIG. 3. In this arrangement the PC 10 includes a display card (not shown) having a digital to analog (D/A) converter 12 to output analog display signals, at a frequency and resolution set by the PC, to an A/D converter 24 of a single scan CRT monitor 22. The output of the A/D converter 24 is supplied to a scaling engine 26 that converts the digital display signals into a frequency and resolution that are compatible with the CRT monitor 22 and supplies them to a D/A converter 28. The analog output display signals of the DIA converter 28 are supplied to the monitor 22 for display at a resolution and frequency compatible with the monitor. The disadvantages of this arrangement are also that it is complex to manufacture and expensive.
Lastly, in the possible arrangement of FIG. 4, a PC 30 having an internal scaling engine 32 outputs digital display signals at a resolution and frequency compatible with a single scan LCD monitor 16. While this arrangement has the advantage of a lower cost host, the LCD panel is still expensive for general use, e.g. in desktop PCs.
What is needed is a single horizontal scan range monitor, preferably a CRT monitor, that is inexpensive, not complex to make, and allows the monitor to be compatible with PCs having display circuits that output display signals at a variety of different scanning frequencies and display resolutions.
The above and other objectives are obtained by the present invention of a single horizontal scan range monitor that accepts display signals in a digital format from an external source, such as a personal computer. The initial display signals can have one of a plurality of input resolutions and scanning frequencies. A converter supplied with the initial display signals detects the particular input resolution of the initial display signals and converts them to digital output signals having a vertical output resolution selected from a plurality of different output resolutions matched to the detected input resolution of the initial display signals and a horizontal scanning frequency that is the same as the horizontal scanning frequency of the monitor.
Preferably the monitor is a cathode ray tube (CRT) monitor. In some embodiments, the initial display signals are converted to output signals having a single predetermined horizontal resolution, regardless of the horizontal resolution of the initial display signals. In one preferred embodiment, the converter is an integrated circuit chip.
The monitor includes a display data input for receiving the initial display data. This display data input can be a receiver where the external source transmits the initial display data in the digital format. In some preferred embodiment, the converter is a circuit that includes a frame memory. The display signal conversion is accomplished by controlling the data writing and reading rates to the frame memory. The converter includes, in addition to the frame memory, a resolution detector for detecting the resolution of the initial display signals and outputting a resolution detection signal and a first multiplexer connected between the display data input, the frame memory, and the monitor for switching between writing the initial display signals into the frame memory and reading the digital output signals out of the frame memory to the monitor. An address counter controller controls the addresses at which data are written into the frame memory and read out from the frame memory. A vertical sync generator connected to the resolution detector generates a vertical sync pulse for the monitor at a selected one of a plurality of vertical sync frequencies as a function of the detected resolution of the initial display signals. A horizontal sync generator generates a horizontal sync pulse at the single horizontal scanning frequency of the monitor. A data output clock generator generates a data output clock signal as a product of the single horizontal scanning frequency and a multiplier factor equal to the sum of the horizontal output resolution and a horizontal blanking interval.
A second multiplexer receives from the display data input a clock and a vertical sync signal. The second multiplexer is connected to the address counter, the data output clock signal generator, and the horizontal sync generator for selectively supplying to the address counter controller either the combination of the vertical sync signal and the clock from the display data input or the combination of the data output clock signal from the data output clock generator and the horizontal sync pulse from the horizontal sync generator. A sector controller controls the first multiplexer and the second multiplexer to synchronously and alternately write the initial display data to the frame memory at initial resolutions and scanning frequencies and read the digital output data signals from the frame memory to the monitor at resolutions and scanning frequencies that are compatible with the monitor.
In embodiments where the converter resides in the monitor, it is preferable to have the display signals transmitted by the PC to the monitor in digital form. A receiver is incorporated as part of the display data input of the monitor and receives the digital display signals and forwards them to the converter. In the preferred embodiments, the receiver is one of a transition-minimized differential scaling (TMDS) receiver, a low voltage differential signaling (LVDS) receiver, a low voltage differential signaling display interface (LDI) receiver, and a gigabit video interface (GVIF) receiver.
In one preferred embodiment wherein the receiver is a TMDS receiver, the clock from the receiver is a transition minimized differential scaling (TMDS) clock signal. The horizontal sync generator includes a phase locked loop (PLL) circuit for generating the data output clock. In the preferred embodiment, the horizontal sync generator generates horizontal sync pulses at a frequency of 80 kHz. The vertical sync generator generates vertical sync pulses at a selected one of the following frequencies in correspondence with the resolution detection signal: 79.9 Hz, 95.1 Hz, 124.8 Hz, 98.9 Hz, 88.4 Hz, and 75.1 Hz.
The converters of some of the above-discussed preferred embodiments, particularly those wherein the converter is a integrated circuit, convert the resolution of the initial display signals according to the following table:
where xe2x80x9cInputxe2x80x9d is the resolution in pixels of the initial display signals, xe2x80x9cConvertedxe2x80x9d is the resolution in pixels of the display output signals, xe2x80x9cfHxe2x80x9d is the horizontal frequency of the display output signals in Kilohertz, xe2x80x9cfVHzxe2x80x9d is the vertical sync frequency of the display output signals, and xe2x80x9cClockxe2x80x9d is the data output clock in Megaherz (which is computed by multiplying fHxc3x97(horizontal resolution)xc3x97(a constant). In these examples the constant is approximately 1.35.
In still other embodiments, the conversion of the resolution of the initial display signals is according to the following table:
where the constant for computing the Clock is approximately 1.36.
The invention also encompasses the methods embodied in the processing steps carried out by the elements of the above described single horizontal scan range monitors.